This invention relates to four-cycle internal combustion engines and more particularly to an improved variable valve timing control and journalling arrangement for the camshafts of such an engine.
It has been recognized that the performance of an engine can be improved through a wide variety of engine speeds and loads by employing a variable valve timing (VVT) mechanism. In this way, the valve timing can be optimized for the particular running condition so as to provide the desired performance. Generally, the variable valve timing mechanism is interposed in the drive of the camshaft from the engine crankshaft and frequently is mounted on one end of the associated camshaft. When twin overhead camshafts are employed, it is common to have the variable valve timing mechanisms at the same end of the respective camshafts.
In order to perfect the control, it is also necessary or desirable to have a sensor associated with each of the camshafts so as to sense the angular position of the respective camshaft. Various arrangements have been proposed for mounting the camshaft sensor and those methods, which have been proposed, have some disadvantages.
In accordance with one method, the camshafts have a timing wheel or the like mounted at one end thereof, normally the end opposite from the variable valve timing mechanism. A sensor is fixed to the engine body adjacent this timing wheel so as to provide the signal indicative of the camshaft position.
One way in which the sensor may be mounted is by supporting it from the bearing cap for this end of the camshaft. This means that the camshaft is elongated beyond the bearing surface so as to accommodate the mounting of the timing wheel and associated sensor. This presents problems inasmuch as the engine is elongated by such an arrangement.
Another form of sensor for camshaft angle mounts the sensor on the cam cover of the engine. However, this is a rather imprecise way of monitoring the position due to the fact that the cam cover is not always accurately positioned relative to the camshaft or the cylinder head. That is, a sealing gasket is interposed between the cam cover and the cylinder head and this can permit the cam cover and accordingly the sensor to shift relative to the camshaft.
Although keying of the cam cover to the cylinder head can be employed to avoid this problem, this complicates the assembly and nevertheless, there still can be variations in the spacing between the cam cover and the cylinder head even though the axial alignment may be maintained. Also, this keying can generate some engine noise since the silencing of the effect of the gasket is eliminated.
Another way of mounting the sensor is by fastening it directly to the cylinder head itself. However, such mounting may place the sensor in a juxtaposed position to either the intake or the exhaust sides of the cylinder head. This can cause difficulties, particularly undo heating of the sensor if positioned adjacent the exhaust side as generally must be done when the angular position of the exhaust camshaft is being sensed. Also, this can present difficulties in mounting the electrical leads for conveying signals from the sensor to the control for the VVT mechanism.
It is, therefore, a principal object to this invention to provide an improved camshaft sensor arrangement for a four-cycle internal combustion engine wherein the sensor is accurately mounted and does not cause elongation of the engine nor routing problems for the electrical conduits.
It is a further object to this invention to provide an improved and simplified sensor mounting arrangement particularly for multiple camshaft engines wherein each camshaft has a variable valve timing mechanism associated with it.
This invention is adapted to be embodied in a four-cycle internal combustion engine having an engine body with a plurality of axially spaced bearing sections. A plurality of axially spaced bearing caps are fixed to the engine body and cooperate with the bearing sections for journaling axially spaced bearing surfaces of a camshaft. A variable valve timing mechanism is associated with one end of the camshaft for driving the camshaft in an adjustable, timed fashion from an engine crankshaft. One of the journalled camshaft bearing surfaces is juxtaposed to the variable valve timing mechanism. A timing member is formed on the camshaft on the side of the one journalled camshaft bearing surface opposite to the variable valve timing mechanism. A timing sensor cooperates with the timing member for providing a signal indicative of camshaft angle. The timing sensor is carried by the bearing cap that journals the one of the journal camshaft bearing surfaces.